"The zoo life compared to sanctuary life is completely different," Meg McCue Jones, senior animal caregiver at IPPL, tells The Dodo. "We're not getting the normal stressors like the animals would get at a zoo. They're not being gawked at. People running around. People yelling. It's a pretty low-stress environment here."

Before the zoo closed its doors in 1996, Maui - along with his mother, Jade, and father, Palu-Palu - were little more than exhibits.

Just things to be gawked at for the price of admission.

When the zoo shut down - McGreal says over animal welfare violations - the sanctuary negotiated to take the entire family.

The sanctuary is home to more than zoo refugees. There are former lab animals here too, as well as gibbons who survived attempts to turn them into pets. And while the average life span of a gibbon in the wild is around 25 years, many of these residents live much longer. Some have even reached well into their 50s.

None of them look a day over 18.

"Gibbons have a benefit over us humans," McGreal says. "They don't look old."